1. Field
One or more embodiments of the present invention relate to dyes for dye-sensitized solar cells, methods of preparing the same, and solar cells including the dyes.
2. Description of the Related Art
In an effort to address current energy problems, much research is being conducted into alternatives to existing fossil fuel. For example, a wide range of research into natural energy sources, such as wind power, atomic power, and solar power, is being conducted in an effort to replace petroleum resources, which will be depleted within a few decades. Among these energy sources, solar cells using solar energy (unlike other energy sources) provide unlimited energy and are environmentally friendly. A selenium (Se) solar cell was developed in 1983, and thereafter, silicon solar cells have been receiving attention.
However, the manufacturing costs associated with such silicon solar cells are very high, and thus, it is difficult to make them commercially viable, and battery efficiency is difficult to achieve. In order to address these problems, many efforts have been made to develop inexpensive dye-sensitized solar cells.
Unlike silicon solar cells, dye-sensitized solar cells are photoelectric, chemical solar cells mainly composed of a photosensitive dye molecule that absorbs visible light and generates electron-hole pairs, and a transition metal oxide that delivers generated electrons. An example of a known dye-sensitized solar cell is the solar cell developed by Gratzel et al. of Switzerland in 1991. Dye-sensitized solar cells have lower manufacturing costs per electric power unit than conventional silicon solar cells. Due to such low manufacturing costs, dye-sensitized solar cells are considered an alternative to conventional solar cells.
A conventional structure of such a dye-sensitized solar cell includes a conductive transparent substrate, a light absorbing layer, an electrolyte layer, and an opposite electrode, where the light absorbing layer includes semiconducting micro-particles and a dye. An operational method of the conventional dye-sensitized solar cell will now be described briefly. When solar light is absorbed by dye molecules, the dye molecules transition from a ground state to an excited state and generate electron-hole pairs. Excited electrons migrate to a conduction band at an interface between titanium oxide particles and the dye molecules. Injected electrons are delivered to the conductive transparent substrate via an interface between the conductive transparent substrate and the titanium oxide particles and move to an opposite electrode via an external circuit. Meanwhile, the dye molecules that are oxidized by the electron transition are reduced by an ion of a redox couple in the electrolyte layer, and the oxidized ion and electrons arriving at the interface between the opposite electrode and the electrolyte layer participate in a reduction reaction to achieve charge neutrality.
In the operational method described above, the first operation is to generate photo charges from photo energy, and to do this, the dye molecules are excited by absorbing light that is transmitted through the conductive transparent substrate. The dye molecules may include an organometallic complex.
Although such dye molecules have high proton yields, their efficiency in a solar cell is insufficient. Accordingly, there is a need to develop dyes having improved performance.